Insurance - Reconciliation of incurred and paid claims development information to the aggregate carrying amount of the liability for unpaid losses and LAE (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total reserves, net of reinsurance	$ 7,655	$ 7,275	$ 7,208	$ 6,799
Reinsurance recoverables on asbestos and environmental reserves, net of allowance	3,419	3,117	3,024	2,942
Unpaid losses and loss adjustment expenses	11,074	$ 10,392	$ 10,232	$ 9,741
Property and casualty insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Specialty unpaid losses and LAE, net of reinsurance	6,455
Other unpaid losses and LAE, net of reinsurance	1,200
Unallocated LAE	382
Total reserves, net of reinsurance	7,655
Reinsurance recoverables on asbestos and environmental reserves, net of allowance	3,419
Unpaid losses and loss adjustment expenses	11,074
Property and casualty insurance | Foreign operations
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Other unpaid losses and LAE, net of reinsurance	349
Property and casualty insurance | A&E reserves
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Other unpaid losses and LAE, net of reinsurance	408
Property and casualty insurance | Other
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Other unpaid losses and LAE, net of reinsurance	61
Property and casualty insurance | Property and transportation
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Specialty unpaid losses and LAE, net of reinsurance	1,318
Property and casualty insurance | Specialty casualty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Specialty unpaid losses and LAE, net of reinsurance	4,447
Property and casualty insurance | Specialty financial
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Specialty unpaid losses and LAE, net of reinsurance	256
Property and casualty insurance | Other specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Specialty unpaid losses and LAE, net of reinsurance	$ 434